1. Technical Field
The present invention relates to a method and an apparatus for judging an optical disc, and more particularly to a method and an apparatus for judging a blank area and a data-recorded area of an optical disc.
2. Description of the Related Art
As is known to all, the reflectivity of a CD disc or a DVD disc is relatively higher if no data are recorded in the data track. Whereas, if data are recorded in the data track, the reflectivity of the CD disc or the DVD disc decreases. The optical disc having a lower reflectivity in its recorded portion (i.e. a data-recorded area) than in its unrecorded portion (i.e. a blank area) is also referred as a HTL (High to Low) disc. Most of the existing blue ray discs are HTL discs.
On the other hand, some of the blue ray discs are not HTL discs. That is, the reflectivity of such disc is relatively lower if no data are recorded in the data track; whereas, the reflectivity increases if data are recorded in the data track. The optical disc having a higher reflectivity in its recorded portion (i.e. a data-recorded area) than in its unrecorded portion (i.e. a blank area) is also referred as a LTH (Low to High) disc.
Generally, after an optical disc is loaded in a read-only optical disc drive, a focusing-on operation is performed. After the focusing-on operation is performed and before a tracking-on operation is performed, it is necessary to judge whether the laser beams emitted from the optical pickup head are irradiated on the data-recorded area of the optical disc or not. Once the laser beams emitted from the optical pickup head are irradiated on the data-recorded area, the tracking-on operation can be performed. Whereas, if the laser beams emitted from the optical pickup head are irradiated on the blank area of the optical disc, a tracking failure problem occurs.
FIGS. 1A and 1B are schematic timing waveform diagrams illustrating the radio frequency signals obtained from a blank area and a data-recorded area of a conventional HTL disc, respectively. As shown in FIG. 1A, after a HTL disc is loaded in the optical disc drive and a focusing-on operation is performed and before a tracking-on operation is performed, an optical pickup head of the optical disc drive is moved while irradiating the laser beams on the blank area of the HTL disc. As such, a radio frequency signal RF similar to a ripple is obtained. In this situation, the peak to peak value of the radio frequency signal RF is Vpp1. Whereas, as shown in FIG. 1B, if the laser beams emitted from the optical pickup head are irradiated on the data-recorded area of the HTL disc, a radio frequency signal RF having higher frequency is obtained by moving the optical pickup head. In this situation, the peak to peak value of the radio frequency signal RF is Vpp2.
Obviously, the peak to peak value Vpp1 for the blank area is lower than the peak to peak value Vpp2 for the data-recorded area. In other words, the radio frequency signal RF may be compared with a slicing level in order to judge whether the laser beams emitted from the optical pickup head are irradiated on the blank area or the data-recorded area.
The above judging method, however, still has some drawbacks. For example, in a case that the optical disc is a rewritable disc (e.g. RW disc) with low reflectivity change or the intensity of the laser beams emitted from the optical pickup head are too low, an erroneous judgment problem possibly occurs. FIGS. 1C and 1D are schematic timing waveform diagrams illustrating the radio frequency signals obtained from a blank area and a data-recorded area of a conventional low reflectivity HTL disc, respectively. Since the reflectivity difference between the blank area and the data-recorded area is very small, the peak to peak value Vpp3 of the radio frequency signal RF for the blank area and the peak to peak value Vpp4 of the radio frequency signal RF for the data-recorded area are not considerably distinguished. In other words, it is difficult to determine the slicing level, and thus the erroneous judgment problem is readily generated.
Moreover, another method for judging the blank area and the data-recorded area according to a bottom envelop signal is disclosed. FIGS. 2A and 2B are schematic timing waveform diagrams illustrating the radio frequency signals and the bottom envelop signals obtained from a blank area and a data-recorded area of a conventional HTL disc, respectively. Obviously, as shown in FIG. 2A, if the laser beams emitted from the optical pickup head are irradiated on the blank area of the optical disc, the bottom envelop signal BES is identical to the radio frequency signal RF because the frequency of the radio frequency signal RF is relatively lower. In this situation, the amplitude of the radio frequency signal RF is Va1. Whereas, as shown in FIG. 2B, if the laser beams emitted from the optical pickup head are irradiated on the data-recorded area of the optical disc, the amplitude of the bottom envelop signal BES is Va2.
Obviously, the amplitude Va1 of the bottom envelop signal BES for the blank area is lower than the amplitude Va2 of the bottom envelop signal BES for the data-recorded area. As a consequence, the use of a threshold value may judge whether the laser beams emitted from the optical pickup head are irradiated on the blank area or the data-recorded area.
Similarly, in a case that the optical disc is a rewritable disc (e.g. RW disc) with low reflectivity change or the intensity of the laser beams emitted from the optical pickup head are too low, the erroneous judgment problem possibly occurs. FIGS. 2C and 2D are schematic timing waveform diagrams illustrating the radio frequency signals and the bottom envelop signals obtained from a blank area and a data-recorded area of a conventional low reflectivity HTL disc, respectively. Since the reflectivity difference between the blank area and the data-recorded area is very small, the amplitude Va3 of the bottom envelop signal BES for the blank area and the amplitude Va4 of the bottom envelop signal BES for the data-recorded area are not considerably distinguished from each other. In other words, since it is difficult to determine the threshold value, the erroneous judgment problem is readily generated.
The above two methods are illustrated by referring to the HTL disc. Nevertheless, due to the small reflectivity difference between the blank area and the data-recorded area of the LTH disc, the amplitude of the radio frequency signal or the bottom envelop signal is still too low. In this situation, the erroneous judgment problem possibly occurs.
Another method for judging a blank area and a data-recorded area of an optical disc is disclosed in for example Taiwanese Patent Publication No. 1317944, which is entitled “Method for identifying recording contents of an optical disk”. In this method, a radio frequency signal is processed by a low pass filter to generate a filtered radio frequency signal. According to the level of the filtered radio frequency signal, this method may judge whether the laser beams emitted from the optical pickup head are irradiated on the blank area or the data-recorded area. However, this method is illustrated by referring a HTL disc. That is, this method is not suitable to judge the LTH disc.